EMD-type unit injectors are characterized by a nozzle valve body which terminates in a nozzle tip and houses a nozzle valve. The seat for the nozzle valve is formed at or near the nozzle tip and communicates with a small spray hole feed chamber or "sac," just below the seat and within the tip. The lower end of the nozzle valve projects into the sac in both open and closed positions of the valve, projecting somewhat further into the sac in closed position. The sac typically has a cylindrical sidewall and a hemispherical bottom wall. The fuel is distributed through the sac under high pressure to spray holes which are several times longer than their diameter. The spray holes lead from the sac through the wall of the injector tip and into the engine chamber where the fuel is atomized.
As pointed out in U.S. Pat. No. 5,467,924 of common assignee, the disclosure of which is incorporated by reference as if fully repeated herein, the diesel engine industry has been under pressure to reduce noxious emissions. However, achievement of acceptably low rates of noxious emissions is by no means the only concern of the industry. In particular, the industry is also under continuing pressure to improve fuel efficiency. Although the diesel engine is the most efficient internal combustion engine used in motive power, there is continuing economic pressure to further reduce fuel costs, and continuing political pressure from conservationists to reduce the rate of consumption of fossil fuels. These pressures are particularly felt in respect of EMD-type locomotive fuel injectors, a type already widely used and whose use can be widely supported by existing networks of rebuilders as well as original equipment manufacturers.
Therefore, achievement of lower emissions is not enough; improvement in fuel efficiency is also of central importance. Cost of manufacture and reliability of operation must also be taken into account.
The present invention accomplishes these combined objectives, relating to fuel efficiency, emissions reduction, cost, and reliability in a particularly effective manner. The present invention maintains emissions in EMD-type injectors at the lowest levels previously accomplished (or lower), while at the same time improving fuel efficiency, all at no increase in manufacturing costs and no reduction in reliability of operation.
The present invention involves configuring the sac so that its center of volume is located below the center of radius of the sac bottom. This is believed to be a departure from all prior art EMD-type injectors (in which the center of the sac volume has been above the center of radius of the sac bottom). While the reasons for the improved performance of the invention are not fully understood, it is believed that this change in configuration from the prior art results in a more laminar (less turbulent) distributive flow of the fuel through the sac to the spray holes when the nozzle valve is opened by lifting it from its conical valve seat to allow the highly pressurized fuel to flow into the sac. It is believed that the less turbulent flow of fuel into the body sac and especially at the entrance of the nozzle orifices in the sac, provides increased penetration of the fuel spray into the combustion chamber thereby improving the distribution of fuel throughout the combustion chamber for a "more complete" burning of the fuel.
Whatever the complete explanation of the improvement in the spray formation, flow conditions are changed so as to improve fuel efficiency as well as reduce noxious emissions below the best known to have been previously achieved with EMD-type injectors.
In the design of diesel injectors of the type to which the invention relates, maintaining the integrity of the durability characteristics of the nozzle is a primary consideration because performance improvement at the expense of reliability is unacceptable. In this connection, any modifications in sac configuration must be accomplished without any compromise in structural strength of the structure at the nozzle tip. The present invention also contemplates modifications of the nozzle body shape to maintain the required structural strength despite the configuring of the sac so that its center of volume is below the center of radius of the sac bottom.
These improvements will be more fully understood from the following detailed description of the invention.